Each type of coralline has it's own light requirements. If this one is growing mostly near the top, decrease lighting and it will start to die off. If it's near the bottom, ramp up the lighting.
If there isn't a ton of it, try affixing your razor blade to the end of a piece of tubing that will siphon out the flakes as you scrape them, not allowing any to settle. Obviously turn off the pumps for this.
Your best bet is to combine everyone's ideas. Light change, water chemistry change, etc.
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef